(1) Field of the Invention
The present invention relates to a sewage collection and separation tank system and method of construction. Because sewage tanks are usually large in area, the sewage tank floor is preferably built from concrete sections, poured radially around a centrally located sump pump pit. The sections are usually wedge shaped or pie shaped and comprised of a lower face adjacent to an earthen pit or excavation, an upper face parallel to the lower face and first and second sides between the faces. To create a water tight, leak-proof concrete floor for the sewage tank system, it is necessary to ensure that the next section is poured abutting against a wet side of the previous section. When pouring a substantial area of concrete, like a sewage tank floor, it is extremely difficult to get adjoining sides of the first and last sections of the tank floor to seal along their common seam. The first side of the first section will almost always be too dry by the time the second side of the last section is poured to provide a water tight seam between the first and last sections. This can allow fluid held in the tank to leak through the seam and result in pollution which can be economically and environmentally damaging.
As a solution to this problem a first elastomeric gasket is mounted in a groove around the perimeter of the sump pump pit wall. This first gasket is encased in concrete as the sections of the sewage tank floor are poured radially around the sump pump pit and provides an impervious liquid seal between the floor of the sewage tank and the sump pump pit.
A second elastomeric gasket, preferably made of rubber, is mounted in a groove in the first side of the first section of the sewage tank floor so that half of the gasket projects outside of the groove. Regardless whether the concrete at the first side has set-up or dried by the time the last section is poured, the second side of the last section will encase the exposed half of the second gasket, forming a liquid tight seal between the first and last sections. The second gasket thus acts as an impervious member along the seam between the first and last sections and prevents the seepage of liquids held in the sewage tank into the ground below the tank.
Preformed wall panels are mounted in a channel formed around an outer periphery of the tank floor. The wall panels are preferably sealed to the tank floor by a third elastomeric gasket or with a bitumastic compound poured over a non-shrink grout in the channel around the outer periphery of the tank floor. The seal between the wall panels and the tank floor in the channel can also be provided by the third elastomeric gasket in conjunction with a bitumastic compound. The third gasket abuts against the second gasket to provide a seal between the wall panels and the first and last sections of the tank floor. Finally, adjoining wall panels are joined to each other with a joint made of a tongue and a groove provided in the adjoining edges of the wall panels. The tongue and groove joint can be further sealed with a fourth elastomeric gasket, or a sealing compound like tar or an asphalt based compound such as a bitumastic coating over a non-shrink grout or both the elastomeric gasket and the bitumastic coating in conjunction with each other.
(2) Prior Art
The prior art has described various types of concrete holding tanks and concrete pools for holding liquids. However, none of the prior art shows a sewage tank system and method of construction that uses an elastomeric gasket encased between a dry side and a wet side of adjoining poured concrete sections of the sewage tank floor to provide a seal along the seam between the adjoining sections.
The prior art holding tanks and pools are typically built having a unitary concrete floor with side walls made of concrete panels. The concrete panels are mounted side-by-side in a groove formed in the concrete floor. The concrete panels are then sealed to the floor by cast-in-place concrete beams. For added sealing, a water stop sealing material is preferably encased between the concrete floor and the concrete panels and between the side-by-side concrete panels by the cast-in-place concrete. This prior art is illustrated by U.S. Pat. Nos. Re 29,777 to Crowley and 4,126,976 to Crowley.
U.S. Pat. Nos. 3,642,138 to Sheda and 4,550,538 to Blakeway are illustrative of liquid holding tanks that use a sealing strip between a metal surface and a concrete foundation or between two metal surfaces to provide a water tight seal. The sealing strip is usually made of an elastomeric material such as a rubber, although tar and oakum also work well.